The comprehensive growth plan drafted for the six-county Sacramento area says nearly seven of every 10 new local homes built through 2050 should be attached or use small lots -- more than twice the proportion the region has now.

And with land prices soaring, homebuilders here are starting to see some merit to that approach.

The plan was assembled by the Blueprint Project, and the goal of its "preferred scenario" is to shift the region toward higher-density home construction as a way to reduce sprawl, transportation congestion, smog and other perils of uncontrolled growth. The Blueprint Project is a joint effort by the Sacramento Area Council of Governments, a regional transportation planning body, and Valley Vision, a coalition of regional leaders that focuses on planning for the area's future.

The target of the preferred plan is to arrive at the year 2050 with 53 percent of the region's housing in higher densities -- in attached housing such as townhomes or condominiums, or detached homes at eight or more homes to an acre.

Today, 32 percent of homes fall into those higher-density categories, and five homes to an acre is typical. That means 69 percent of new homes built between now and midcentury would have to be at the higher densities to reach the preferred target.

The denser development would not be mandatory unless local governments adopt the guidelines in the preferred plan, but many see that scenario as the best way to subdue increasingly horrendous commutes and preserve breathable air and undeveloped land.

If the region keeps developing according to its current pattern, "it will be an immensely less healthy place to live and less of an economic competitor nationally, because the cost of living will be higher," said David Mogavero, a spokesman for the Environmental Council of Sacramento.

Generally, the homebuilding industry agrees that a major shift to higher density is coming, driven by the shrinking inventory and rising price of land, if nothing else. But builders worry that an overzealous emphasis on one kind of housing over another could hamper the industry's ability to react to consumer desires.

On the other hand, for the first time since idealists began arguing in favor of higher-density growth here, circa 1988, the pragmatic homebuilding industry seems to be nodding in agreement.

"Homebuilders are going to respond to the market, and the market is moving to higher density because land is more expensive," said Dennis Rogers, a spokesman for Building Industry Association of Superior California.

"Are we 100 percent in lockstep with the preferred alternative? No," he said. "But we do support the blueprint process."

1.7 million more people by 2050: The Blueprint Project covers El Dorado, Placer, Sacramento, Sutter, Yolo and Yuba counties. The planning effort was largely prompted by the Sacramento Area Council of Governments' need to prepare transportation plans for the region.

SACOG calculated that the six-county populace may grow by 1.7 million people and 840,000 new homes by 2050. Planners concluded that the area would see awful traffic jams, worsening air quality and a dramatic loss of open space to development unless future communities were planned to better support mass transit and cut the need for trips in private vehicles.

"The preferred scenario is critical for transportation planning," said Mike McKeever, a SACOG planner and the Blueprint Project manager.

SACOG, he said, ran computer projections showing the impact on traffic congestion if current land-use policies continue or if more restrictive ones are followed. The result: Big traffic problems with current policies, but "significant benefits to the transportation system and the airshed" under the preferred scenario, he said.

SACOG staff spent two years on the blueprint, much of it meeting with local residents and officials to pursue a consensus on a preferred plan. That scenario has been drafted, and it will be presented in December for adoption by SACOG's board, composed of elected officials from the region's local governments.

The preferred scenario calls for the extensive use of "smart growth" planning, meaning zoning for higher-density housing and a mix of uses, optimally concentrated around mass-transit lines to spur ridership for the transit.

It is sharply different from standard planning in the region, which emphasizes large-lot subdivisions that are relatively distant from stores and services.

Among other effects, the preferred scenario's smart-growth strategy would:

Put 38 percent of new jobs within a 15-minute walk of transit, compared to 5 percent if current development patterns prevail

Put 56 percent of the newcomers in areas that have a good balance of jobs and housing, as opposed to 26 percent if current practices continue

Put 70 percent of the newcomers in pedestrian-friendly neighborhoods, compared to 34 percent

Allow 40 percent of the homes to be built in infill locations instead of undeveloped "greenfield" sites, compared to 27 percent.

Squeezing 'em in: The preferred scenario is one of several generated at SACOG's meetings, and the one that SACOG found was the most acceptable to the attendees.

It calls for 34 percent of all housing in the six counties by 2050 to be attached rental or for-sale units, up from 29 percent today. It also proposes that 18 percent of stand-alone houses get built on lots of one-eighth acre or less, versus 3 percent today. The balance -- 47 percent -- would be stand-alone homes on larger lots or rural houses, compared to 68 percent today.

To reach those goals, some 39 percent of the 840,000 homes to be built in the region would have to be attached units, and 30 percent would be small-lot, detached houses, McKeever said.

That works out to 327,000 and 252,000 homes respectively.

"It is important," he added, "that people understand these are a regional average and the numbers vary by area. It's not a one-size-fits-all template."

One advantage to the preferred alternative -- beside better transportation planning -- is that it would use 13.2 million acres of open space for development, while existing land-use practices could use almost 29 million acres, SACOG estimates.

Assuming the SACOG board adopts the plan, it would stand as a model for municipalities to choose or reject when they approve new communities.

Builders turn a conceptual corner: About a decade ago, when Sacramento County planners suggested large amounts of higher-density housing for the county general plan, "homebuilders went ballistic and fought it very aggressively," said John Schleimer, head of Market Perspectives, a local company that studies the new-home market.

Back then, the overwhelming demand was for homes on lots zoned RD-5 -- five houses per acre at most. There was plenty of cheap land, so there was no problem providing lots that big.

This time around, the builders are more amenable to the concept of higher density, because rising land costs and development constraints have pushed new-home prices through the ceiling, said John Hodgson, a land-use attorney who helps process some of the region's biggest developments.

Many builders have already begun increasing the density of their developments to keep home prices down.

"Builders realize that because of land constraints, we're headed to higher density," said Brendan O'Neill, chief financial officer for Beazer Homes of Northern California. "But I doubt if anyone expected it to happen this quick. I doubt if my children's first home will be an RD-5 lot in suburbia. I see it as an attached townhome. Maybe later they'll move to suburbia."

More than 40 percent of the 5,000 homes Beazer is planning will be attached or smaller-lot detached, he said. "We accept the preferred alternative as the current political will in the community, and we are heading towards it because we think similarly -- the future is in higher-density homes."

In other words, the cost of land is driving the industry toward the thinking of regional planners. Nonetheless, homebuilders are manufacturer-merchants, so some worry that ideas from the blueprint might crimp their market.

Well, sort of: For example, although O'Neill supports the preferred scenario, he worries that too many high-density units will be brought to market at the same time.

"Detached homes are preferred by the buyers," said Bill Heartman, president of Regis Homes of Northern California and one of the most successful builders of high-density, detached houses. "We can achieve almost the same densities with detached as we can with attached."

He agreed that high-density is the trend, but he does not want to be forced to build attached homes if demand does not warrant it, he said.

New-home market analyst Schleimer argued that the future housing mix should include fewer attached homes and more small-lot detached houses. "We're starting to get more acceptance of attached, but that (preferred alternative) may be too aggressive for our marketplace," he said.

The exception would be if detached homes became so pricey that attached housing became the only affordable alternative, and that's increasingly possible, Schleimer added.

The price of an average new home in the region reached $460,413 in the third quarter, according to The Gregory Group, another analyst of the new-home market.

Although the industry generally supports the preferred alternative, builders worry that "municipal decisions become proscriptive," said building industry representative Rogers.

If the municipalities, he said, really want higher numbers of high-density homes, they should work to remove barriers to that type of construction and provide incentives. But local government should not force certain types of housing on unwilling consumers.

"We are in transition, going to higher density," he said. "But we don't want to inject policies in the market that upset the natural ebb and flow of the market."

Customers may soon prefer more density in their housing. SACOG's McKeever pointed out that a recent study commissioned by the Sacramento Metropolitan Chamber of Commerce estimated that two-thirds -- about 1 million -- of the region's population growth by 2050 would be in people 55 or older.

Of those, one-third would likely prefer attached homes, another third would want small lots, and one-third prefer large lots, the study estimated.